The Unmountable Boot volume blue screen is probably the most common blue screen error message that I see often. This is Windows way of telling you that it is having a problem booting up.

Solution:

The solution to this problem is to boot your computer with the Xp CD-ROM. (Each manufacturer has a different method of booting from the CD-ROM drive, please refer to your computer manufacturer documentation on how to boot from the CD-ROM drive)Once the computer has booted from the cd, let it run until you get to the "Welcome to Setup" screen.

From the "Welcome to Setup" screen press the "R" button on your keyboard, this will put us in the Recovery Console. The Recovery Console will now give us the choice of what operating system that we would like to load, you will be looking for drive c: and on most computers this will be choice 1.The next step will ask you for your administrator password, Enter your administrator password at this time or leave it blank if your administrator account does not have a password and press the "Enter" button. You should now be left with a black screen with c:/ were you will type in "chkdsk c: /r" without the quotation marks and press the "Enter" key.This will start the checkdisk process that can take anywhere from 30 minutes to a couple hours to complete.After the operation has completed type "exit" to reboot the machine. (Don't forget to remove the Windows XP cd from the CD-ROM drive) This usually works for me about 90% of the time when the Unmountable Boot Volume blue screen was caused by a filesystem or BOOT.INI corruption.